1.1 DESIGN CONDITIONS :
This paragraph defines the temperatures, pressures, and forces applicable to the design of piping, and states the considerations that shall be given to various effects and their consequent loadings
.
1.1.1 Design Pressure :
The design pressure of each component in a piping system shall be not less than the pressure at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service.
1.1.2 Design Temperature :
The design temperature of each component in a piping system is the temperature at which, under the coincident pressure, the greatest thickness or highest component rating is required.
1.1.3 Design Minimum Temperature :
The design minimum temperature is the lowest component temperature expected in service.
1.1.4 Bases for Design Stresses :
The bases for establishing design stress values (allowable stress values) for metallic materials in this Code are as follows.
Basic allowable stress values at temperature for materials not exceed the lowest of the following :
1. the lower of one-third of SMTS and one-third of tensile strength at temperature;
2. the lower of two-third of SMYS and two – thirds of yield strength at temperature;
2.2 WELD JOINT QUALITY FACTOR, E
J:
Basic Quality Factors. The weld joint quality factors Ej tabulated in Table A-1B are basic factors for straight or spiral longitudinal welded joints for pressure-containing components as shown in Table 302.3.4
Increased Quality Factors. Table 302.3.4 also indicates higher joint quality factors which may be substituted for those in Table A-1B for certain kinds of welds if additional examination is performed beyond that required by the product specification.
2.3 PRESSURE DESIGN OF COMPONENTS :
2.3.1 Straight Pipe :
The required thickness of straight sections of pipe shall be determined in accordance with following equation.
tm = t + c
The minimum thickness T for the pipe selected considering manufacturer’s minus tolerance, shall be not less than tm.
The following nomenclature is used in the equations for pressure design of straight pipe.
tm = minimum required thickness, including mechanical, corrosion, and erosion allowances.
t = pressure design thickness.
c = the sum of the mechanical allowances (thread or groove depth) plus corrosion and erosion allowances.
T = pipe wall thickness (measured or minimum per purchase specification
d = inside diameter of pipe.
P = internal design gage pressure.
D = outside diameter of pipe as listed in tables of standards or specification or as measured.
E = quality factor from Table A-1A or A-1B S = stress value of materials.
Y = coefficient from Table 304.1.1, valid for t < D/6 and for materials shown. The value of Y may be interpolated for intermediate temperatures.
For t > D/6,
d + 2c Y =
---D + d+2c Straight Pipe Under Internal Pressure :
For t < D/6, the internal pressure design thickness for straight pipe shall be not less than that calculated in accordance with Eq. (3a) :
PD t =
---Following Equation may be used instead of above equation
PD
t =
---2SE
For t > D/6 or for P/SE > 0.385, calculation of pressure design thickness for straight pipe requires special consideration of factors such as theory of failure, effects of fatigue, and thermal stress.
2.3.2 Blanks :
The minimum required thickness of a permanent blank (representative configurations shown in Fig. 304.5.3) shall be calculated in accordance with Eq. (15)
3P
tm = dg --- + c √ 16SE
where-dg = inside diameter of gasket for raised or flat face flanges, or the gasket pitch diameter for ring joint and fully retained gasketed flanges.
E = same as defined earlier.
P = design gage pressure S = same as defined earlier
c = sum of allowances defined earlier.
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2 . MATERIALS
Generic Description:
Classification of materials by generic description involves the grouping of materials into broad categories according to certain attributes such as general composition, mechanical properties, product form, or end use.
There are no precise rules governing which attributes to apply in defining material groups, and the level of detail afforded the classification system depends largely on the level of detail needed to communicate specific ideas. Consequently, materials may be generically grouped according to very broad characteristics, for example metal or nonmetal, ferrous or nonferrous, or cast or wrought. Alternatively, materials may be placed in more narrowly defined generic groups such as mild steel, 3XX series stainless steel, or NiCrMo alloy.
With piping materials, generic grouping based on alloy content is most popular. These groups usually reflect the primary alloy content, and may include varying levels of complexity depending upon the extent to which one needs to communicate specific material needs. Table-5.1 gives an indication of the progression from simple generic descriptors, to complex generic descriptors, which may involve some elements of a standardized classification system (e.g., 300 series austenitic stainless steel).
Table 5.1 Levels of Generic Classification of Materials
Simple Intermediate Complex
Carbon Steel Low Carbon Steel Fully Killed, Low Carbon Steel Low Alloy Steel Cr-Mo Steel 2 ¼ Cr-1Mo Steel
Stainless Steel Austenitic Stainless Steel 300 Series Austenitic Stainless Steel
Nickel Alloy High Nickel Alloy NiCrMo Alloy
Generic material descriptions are frequently used during the early stages of a project, including project definition, conceptual design, front end design, preliminary design, process design, and/or budget estimation. For materials selection purposes during these stages, the user must be aware of Code requirements, but is not looking for a precise solution for each piping system.
Rather, the user should be looking at more global issues including resistance of generic material groups to various forms of corrosion, material cost and availability for various product forms, delivery times, need for qualification testing, and existence of suitable forming and joining technology.
Although there are definite commercial reasons for the existence of trade names (e.g., typically to induce purchasers to specify and buy only the product of a particular manufacturer), many manufacturers and trade associations publish trade name equivalency charts. Consequently, there is usually no need to restrict material selections through use of a single trade name. However, two exceptions do exist where it may be necessary to specify materials by trade name. The exceptions are:
a. Materials of very recent development, still be protected by patent right, and
b. Sophisticated materials required for very severe service situations, where all potential manufacturers may not be equally capable of making the same quality of product. (For certain high alloy materials, minor chemistry or processing modifications can dramatically affect alloy performance.)